Microsporidia are ubiquitous parasites causing infections in insects, fish, and mammals. Microsporidia have recently been demonstrated to infect man. These organisms cause ophthalmic and gastrointestinal infections, primarily in patients with AIDS. Several genera of human pathogens have been cultivated in cell culture. At present there are no data regarding the ability of the human pathogens Encephalitozoon intestinalis and Encephalitozoon hellem to survive under various environmental conditions, nor are there reports regarding the effects of disinfectants on spores of these two species. The survival of microsporidial spores after exposure to disinfectants such as chlorine, alcohol, and quaternary ammonium compounds or to environmental conditions such as elevated temperature and desiccation will be studied. Cultivation of microsporidia in the shell vial system using various cell lines has been investigated. Microsporidia appear to replicate in both fibroblast and epithelial cell lines. Staining methods are being evaluated to detect microsporidial inclusions in infected cell cultures after exposure to disinfectants and environmental conditions. In an effort to replace staining of infected cell cultures, a method for quantitation of microsporidial DNA has been developed. This assay utilizes polymerase chain reaction and a europium-labeled DNA probe.